Cone-like rectification properties of cGMP-gated channels in transmutated retinal photoreceptors of nocturnal geckoes.

Vittorio Vellani,Chiara Giacomoni

doi:10.1155/2014/942510

Vittorio Vellani, Chiara Giacomoni

Open Access

https://doi.org/10.1155/2014/942510

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Abstract

Photoreceptors of nocturnal geckoes are scotopic, with rod-shaped outer segments, and sensitivities to light similar to the one of retinal rods from other species of lower vertebrates. However, these cells are not rods, but they originated from cones of ancestral diurnal geckoes with pure-cone retinas, after being forced to adapt to a nocturnal behavior. Several interesting adaptations of these rod-like cones have been studied to date; molecular biology and functional studies confirmed that several proteins of the phototransductive cascade display structural and functional properties that indicate their origin from cones rather than from rods. In this paper, we investigate, with whole cell voltage clamp in the photoreceptor detached outer segment preparation, the voltage rectification properties of cGMP-gated channels in three species, Gekko gecko, Tarentola mauritanica, and Hemidactylus frenatus. We show that the current-voltage properties in the physiological voltage range are reminiscent of the ones of cGMP-gated channels from cones rather than from rods of other cold-blooded vertebrates. The origin and the relevance of the mechanisms investigated are discussed.

Highlights

The nature and the molecular origin of the differences between rod and cone function represent a highly relevant question in the study of phototransduction in vertebrates
The Scientific World Journal properties of the light-sensitive current in the detached photoreceptor outer segment preparation (DOS) in three nocturnal gecko species, Gekko gecko, Tarentola mauritanica, and Hemidactylus frenatus and we show that current-voltage study displays cone-like features in the physiological voltage range
The inward rectification properties of the cGMP-gated channels expressed in cones

Summary

Introduction

The nature and the molecular origin of the differences between rod and cone function represent a highly relevant question in the study of phototransduction in vertebrates. Photoreceptors of nocturnal geckos, despite the rod-like shape, ultrastructure, and function [1,2,3], are cones evolutionarily adapted to fulfill the role of rods and allow scotopic vision This hypothesis was originally proposed by Walls and it is known as “transmutation theory” [4, 5]. Because of their intermediate physiological properties between rods and cones, photoreceptors from nocturnal geckos represent an outstanding model for the investigation of the physiological and molecular differences between these cell types, which may lead to general quantitative and qualitative cues on the mechanisms of phototransduction.

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